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Thread: Best Equipment for PLC

  1. #11
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    Quote Originally Posted by Dennis Alwon View Post
    If one were to learn PLC logic what would be he best equipment to learn- ie, the most popular I guess...What would that be and where would you go to learn it.
    AB. it's still the de facto standard in industrial control PLC's, because of the manufacturer support.
    overpriced, until you have a process line down, and can't get support or parts.

    RLL, relay ladder logic, is still the backbone of this, as electricians can follow it.

    dynamic logic is coils operating switches, and switches operating coils.

    RLL is each rung in the ladder is a true/false statement. true is 1. false is 0.
    the beauty is that it's a logic statement, not a continuity path. no isolating
    inputs, or backfeeds.

    and, or, not, memory, delay, and registers covers an awful lot of what you'll use it for.

    as was said, you can buy a cheap plc, and some software, and largely teach
    yourself.
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  2. #12
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    We have equipment that uses GE Fanuc hardware, automation direct hardware and AB. I've been doing all of our PLC work for years with the exception of AB which was all at one particular location and contracted out. I learned on AD, later got into GE and just now getting into AB.

    If you want to learn on the side, the Do-More line from automation direct is great because the software is free and includes a simulator on your PC. Allen-Bradley is where the money is I would think though. I hated GE to start with but am really found of their new stuff.

    Funny, the guy that did all of our AB work quit from the contractor he worked for. He was trusted to maintain all of the documentation and programs on the work he did because nobody on our end understood any of it. We got a letter from his boss saying, "sorry, we don't have anyone else that can help you. We also can't provide any documentation on the work previously done either. Good luck."
    Deserve's got nothin' to do with it.

  3. #13
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    Brand names aside, generally ladder logic is ladder logic. It's the other stuff that varies in level of complication from one line to another. Communications, handling of numbers, instructions set such as math functions, etc.
    Deserve's got nothin' to do with it.

  4. #14
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    All PLC programming can be thought of as basically similar, so it's true that if you learn one, you can pick up another one. But A-B has about a 60% market share for PLCs in North America at end users. Siemens is #2 with around 19%, then Schneider (Sq. D) at 5%; all others are less than that. That's why a lot of people learn A-B PLCs, because basically no matter where you go, you can get work. I cut my teeth on A-B 40 years ago, my skill set is still somewhat relevant. I had a job for a while that was 100% Siemens up until about 8 years ago and did fine while I was there but I had to "re-learn" everything I thought I knew. Since then I lost track of it until last month when I had to help someone and couldn't even navigate in Step 7 software any more. Yet when I walk up to an A-B system that I have never seen, I know where I am because even after 40 years, much of the operating structure and idiosyncrasies are the same.

    Having been an electrician, then PLC guy, then Engineer, I can attest to the fact that I made more money (because of OT) as an electrician than as a PLC programmer. BUT, I was in a nice air conditioned office, got to go home at the end of the day without stinking when I got there, and I was never laid off as a PLC programmer (whereas I have been laid off as an electrician and as an engineer). I just found it a bit too dull for my taste.
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  5. #15
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    I’ve never found it dull. Stressful as all get out, but maybe that’s more in figuring out how everything is supposed to work together to begin with.
    Tom
    TBLO

  6. #16
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    190507-2222 EDT

    For what I believe is a good history of the early PLCs see
    https://www.automation.com/automatio...controller-plc

    What has evolved into the AB controller was invented here in Ann Arbor, more correctly probably Dexter or Saline, at a company called Information Instruments Inc (3-I). The name John Dute of 3-I rings a bell, but I don't believe I ever met him. I have some vague recollection that I may have talked with him by phone at some much later time.

    It should be noted that in the late 1960s there were no microcomputers. But, by the late 1960s there were digital integrated circuits that performed computation functions. Such as the 74181 and there were very limited memory chips. Memory chips of some good size, like 1024 bits, did not arrive until about 1970. The Intel 4004 was the first integrated digital computer. See
    https://www.intel.com/content/www/us...ntel-4004.html Prior to this were dedicated calculator chips. I believe the early Modicon used core memory to obtain non-volatile memory, one of the GM specifications.

    There were RTL (resistor transistor logic) chips starting in early 1960s. By mid 1060s the TTL design was created to reduce noise susceptibility. Reasonably available by about 1967 or 8 at not too high of a price..

    The 4004 did not exist when the first PLCs were developed. Thus, various simple integrated circuit devices were combined to do the required functions.

    The Intel 8008 came along about early mid 1970s, the 8080 followed, and then the 8086 about 1978.

    Early PLCs used a fixed time length scan cycle. You needed to know how the memory was scanned, or you could make logic mistakes. This should still be the case.

    In the past Modicon had a transitional contact, and AB did not. This was a very useful function.

    AB had a sequencer mode, as well as a combinatorial mode. For most machine control applications I think the sequencer mode is a bad choice.

    To learn PLC programming get a PLC, and its manual, and a book on logical circuits, then play.

    Also see https://en.wikipedia.org/wiki/Invent...grated_circuit

    .
    Last edited by gar; 05-08-19 at 12:32 AM.

  7. #17
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    The inability to be able to save symbol and description names to the PLC was a major PIA with older AB.
    No documentation would be even a bigger PIA.

    Occasionally I have to go back to something I did years ago and have to retrace my steps as to why I did what. I hate to think about following up someone else.
    Tom
    TBLO

  8. #18
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    Simple inputs/outputs all one really needs to know is the mentioned ladder relay logic. One PLC to another may have some minor differences but all is based on that ladder logic.

    More complex logic functions, use of digital or analog input/outputs still probably is similar across the industry, but maybe a little harder to pick up for some people. But if you can read and even draw somewhat complex wiring diagrams, simple ladder logic used is easy to catch on to. You might get away with breaking logic rules in a hand drawing where the PLC will have certain rules that must be followed pretty strictly. Logic generally must read from left to right, one load per line is sort of common rule. Number of aux contacts per component is somewhat unlimited - compared to hard wired applications, software may still put a limit but is pretty high.
    I live for today, I'm just a day behind.

  9. #19
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    Automation Direct, you can download programming software free and write programs right now if you wanted.

    But unless you actually upload and run a program on an actual controller it is difficult to know how successful your outcome was. They have some pretty inexpensive controllers if you want to purchase one to play with. May only have 4-6 inputs 4-6 outputs - relay type, no special function digital/analog I/O's but they can be added on.
    I live for today, I'm just a day behind.

  10. #20
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    Quote Originally Posted by kwired View Post
    Automation Direct, you can download programming software free and write programs right now if you wanted.

    But unless you actually upload and run a program on an actual controller it is difficult to know how successful your outcome was. They have some pretty inexpensive controllers if you want to purchase one to play with. May only have 4-6 inputs 4-6 outputs - relay type, no special function digital/analog I/O's but they can be added on.
    Get a Cmore Micro HMI while you're at it and have even more fun. Ethernet connection ability for both is worth the money. You can have both programs running make changes as you need and see the results without leaving the kitchen table.
    Tom
    TBLO

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